Supertech Plastics - Services - Blow Moulding

By: Ian Brown  11-11-2011
Keywords: Plastics, Plastic Bottles

What is Blow Moulding?

Extrusion Blow moulding

Extrusion Blow moulding is a highly versatile process, where very unique shapes, sizes and neck types can be achieved, using a variety of plastics. This versatility gives an overwhelming advantage over other bottle manufacturing processes.

Extrusion Blow moulding is the process of manufacturing hollow plastic bottles by melting plastic resin and extruding a tube which is then clamped inside 2 halves of a water cooled mould. When the tube of molten plastic is in the mould it is then inflated using pressurised air to the shape of the mould. While inside the mould, the plastic will freeze off to the shape as it is forced against the inside of the mould. The mould will then open releasing the bottle so that the process can be repeated.

The plastics that can be used in the Extrusion Blow moulding process include:

PE – Polyethylene

  • Polyethylene is the most common of resins that are used in blow moulding.
  • These generally consist of HDPE (high density polyethylene) which will produce components with high stiffness, good resistance to water vapour and excellent resistance to alcohol, acids and alkali’s.
  • In its natural state it will produce bottles that are opaque.
  • Various MDPE (medium density polyethylene) bottles can also be achieved which will give bottles more squeezability.
  • High gloss HDPE can be used were a very high gloss finish to the bottle is required.
  • PCR (post consumer recycled) material is now also becoming more common as it utilises recycled HDPE offering a more environmentally friendly alternative.

PP – Polypropylene

  • Polypropylene is widely used in producing bottles where an increased amount of squeezability is preferred ( when the bottle is squeezed the bottle will return to its original position).
  • Bottles blown using polypropylene will give excellent stress crack resistance, and excellent resistance to alkalis and acids.
  • In its natural state it will produce bottles with very good clarity.
  • As polypropylene has a high heat distortion it also makes it suitable for ‘hot filling’.

PETG/PCTG -Polyethylene Terephthalate Glycol

  • PETG is used where very high clarity is required (comparable to a glass bottle).
  • Bottles blown using PETG will give excellent stress crack resistance.
  • PCTG is an alternative to PETG with the advantage of being able to blow more difficult shape bottles than would be achievable using PETG.

PVC – Polyvinyl Chloride

  • PVC is used where clear bottles are required.
  • PVC bottles will give very good resistance to alcohols, acids and alkalis.
  • Frosted PVC can also be used.

K-Resin SBC:

  • K-resin is ideally suited to a wide variety of packaging applications by virtue of its sparkling clarity, high gloss, and impact resistance.
  • K-Resin, a styrene derivative, is easily processed on polyethylene equipment.
  • It is suitable for packaging many products but is specifically incompatible with fats and unsaturated oils or solvents.
  • This material is frequently used for display and point-of-purchase packaging

Keywords: Plastic Bottles, Plastics

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